1. Field of the Invention
This invention pertains broadly to the area of spectroscopic systems and imaging spectrometry where multiple images of an object are formed corresponding to different spectral components of the object. More specifically, the invention relates to a novel imaging spectrometer designed to acquire simultaneous, spectrally-discrete, two-dimensional images in real time while maintaining the spatial integrity of the image without using scanning mechanisms or mathematically intensive reconstruction/registration algorithms.
2. Description of the Related Art
Spectroscopic systems are optical systems that allow for the determination of the spectral (wavelength) composition of objects and scenes. Generally, these systems collect the total energy coming from the object. The wavelengths that comprise the collected energy are separated with the use of a dispersive element employing refractive means such as a prism or diffractive means such as a grating. After passing through one of these dispersive elements, the different wavelength components of the wavefront propagate in different directions and their intensities are recorded by a one-dimensional array of detector pixels.
Fairly complicated spectroscopic systems have been developed in the prior art. For example, U.S. Pat. No. 5,149,959 and No. 5,276,321 describe multichannel systems for the detection of the wavelength composition of an objects. U.S. Pat. No. 5,251,008, No. 5,561,521, No. 5,461,477, No. 5,225,888, and No. 5,059,026 employ interferometric methods for determining the spectral content of an object or scene. U.S. Pat. No. 4,743,112 and No. 5,260,767 disclose elaborate examples of systems wherein an imaging component forms the image of an object onto a slit aperture and the resulting one dimensional line image is collimated by a lens and dispersed by a grating or prism in a direction perpendicular to the line image. The dispersed light is then imaged onto a two-dimensional detector array.
U.S. Pat. No. 5,216,484 describes an acousto-optic tunable filter-based imaging spectrometers. U.S. Pat. No. 4,134,683 uses multiple channels, where each consists of a lens system, a spectral filter and a detector array. U.S. Pat. No. 4,268,119, No. 4,084,180, No. 4,072,405 and U.S. Pat. No. 4,916,529 use a single optical system in conjunction with a multiple prism assembly. U.S. Pat. No. 5,414,458 utilizes cube beamsplitters instead of prism assemblies. U.S. Pat. No. 4,281,339 and No. 4,531,054 utilize a series of dichroic beamsplitters to propagate the incident light in different directions.
U.S. Pat. No. 4,650,321 discusses a multiple detector system where two detector arrays are used in combination with a dispersive imaging system. U.S. Pat. No. 3,720,146 describes the use of four lenses arranged in a parallelogram configuration to simultaneously produce four images on a film plane. U.S. Pat. No. 5,479,015 also implements multiple focusing members to form a plurality of identical images on a single detector array. U.S. Pat. No. 4,141,625 discusses the use of two partially reflecting mirrors in combination with a single lens system to create two images of an object on a single detector array. U.S. Pat. No. 4,272,684 uses a reflective prism configuration to function as a beamsplitter.
Filter wheel systems have also been used as a means of obtaining spectral images using a single detector, as disclosed in U.S. Pat. No. 5,587,784. U.S. Pat. No. 4,933,751 describes a tri-color separating system which uses four dichroic beamsplitters to form three separate color images right next to each other at an image plane. U.S. Pat. No. 4,786,813 disclose a method for producing two-dimensional, spectrally discrete images on a single detector array by employing a segmented concave mirror. Finally, U.S. Pat. No. 5,024,530 discusses a telecentric, filtered imager capable of producing only two spectral images of an object; U.S. Pat. No. 5,642,191 discloses a very similar approach. U.S. Pat. No. 5,526,119 utilizes multi-faceted prisms to overcome the limitation of two-band imaging and obtain more images.
These prior-art systems are not capable of performing two-dimensional, real-time imaging spectrometry; many require mechanical or electrical scanning and often also require application specific, computationally intensive, system matrices. Therefore, there is still a need for an imaging spectrometer that does not suffer from these drawbacks. This invention is directed at providing an apparatus and a related spectrometric approach to fulfil that need.